You don't have to mess with timetous or intervals. Its pretty simple actually from my point of view, considering I got everything right.

Once you got document.ready grab the current timestamp. Let it be documentReadyAt.

Once jquery was loaded grab the current timestamp again. Let it be jqReadyAt.

Compare the jqReadyAt against documentReadyAt and find the difference. If jQuery already exists the difference will be insignificant. A matter of couple milliseconds. If jquery had to be loaded will be more than 100ms to few seconds.